This proposal describes a five-year career development program to prepare the candidate, Dr. Paul Burridge, for a career as an independent investigator. This program will build on Dr. Burridge's background as a stem cell biologist by providing expertise in molecular cardiology and pharmacogenomics. The mentor is Dr. Joseph Wu, a Professor of Medicine/Cardiology and Director of the Stanford Cardiovascular Institute at Stanford University. The proposed mentor is a physician scientist with significant expertise in stem cell biology and is an expert in cardiovascular disease modeling. The K99 phase will consist of structured mentorship by the primary mentor, complementary meetings with the advisory committee, formal coursework, a provocative research project, and a program of career transition. Doxorubicin is a well-established and highly effective chemotherapy drug commonly used to treat multiple cancers such as lymphoma, leukemia, ovary, lung and breast cancer, but its use is limited by a serious side effect: doxorubicin causes toxicity in cardiomyocytes, causing damage to the heart. Cardiotoxicity can range from asymptomatic reductions in left ventricular ejection fraction (LVEF) to highly symptomatic (Class III to Class I) heart failure. Acute doxorubicin-induced cardiotoxicity occurs in ~11% of patients and long-term cardiotoxic side effects, which can manifest up to 10 years after treatment, are observed in up to 36% of patients. Currently we cannot predict which patients will develop cardiotoxicity and, at present, oncologists do not assess patient-specific genomic data before deciding on doxorubicin dose. Existing strategies for reducing doxorubicin-induced cardiotoxicity (DIC) include (i) reducing dose, potentially reducing chemotherapeutic effectiveness, (ii) development of less cardiotoxic anthracycline analogues, or (iii) co- treatment with a cardioprotective agents such as dexrazoxane, although this has not proven effective and is not currently endorsed by the American Society for Clinical Oncology outside of clinical trials. A major hurdle in filling the significant gaps in our knowledge about the mechanisms of cardiotoxicity and how best to prevent it has been that there are no good human models, due to the inaccessibility of adult human cardiomyocyte patient samples, and the difficulty in isolating and maintaining cardiomyocytes in vitro. Animal models are limited by significant functional disparities between animal and human cardiomyocytes. This hurdle has now been overcome by the recent advances in the generation of human induced pluripotent stem cells (hiPSCs) where a patient's somatic cells can be reprogrammed to pluripotency and maintained indefinitely in vitro. These pluripotent cells can then be efficiently differentiated into cardiomyocytes and further studied in detail. In preliminary studies, Dr. Burridge has developed and validated a set of tools for assessing DIC in hiPSC-derived cardiomyocytes (hiPSC-CMs). Dr. Burridge has established that hiPSC-CMs, derived from patients who have developed DIC, accurately recapitulate the susceptibility phenotype in vitro. By meta-analysis of single nucleotide polymorphism (SNP) studies in patients, generated by our collaborators and others, Dr. Burridge has identified SNPs in two genes that are predicted to be highly associated with DIC (P=10-9 or 10-5). However, before any SNP can be utilized in clinical practice, its validity must be confirmed through studies linking that SNP to a mechanism for DIC. In this proposal Dr. Burridge intends to use the hiPSC-CM model to perform detailed characterization of the function of these genes identified through SNP studies in DIC. During the K99 phase Dr. Burridge will generate hiPSC lines with the two highest probability candidate SNPs (Aim 1). Dr. Burridge will then use the assays established in the pilot study to assess the effect of these SNPs on susceptibility to DIC and also isogenic hiPSC lines genetically modified to over-express or knock- down the whole genes identified to confirm the mechanism of each gene variant (Aim 2). During the R00 phase Dr. Burridge will expand this work to validate 15 additional high-risk SNP hits (Aim 3) to ultimately develop a high-throughput platform for screening cardiotoxicity of novel anthracycline analogues and cardioprotective agents in a patient-specific manner (Aim 4). The overall aim of this proposal is to use patient-specific hiPSC-CMs to help elucidate the mechanisms through which these SNPs affect cardiotoxicity. Dr. Burridge's ultimate goal is to use this information to develop novel therapeutic modalities for the prediction and prevention of chemotherapy-induced cardiotoxicity. In addition, this work will provide a foundation for future studies using patient-specific hiPSC to study the mechanism of other chemotherapeutic agents with cardiac toxicity, e.g. tyrosine kinase inhibitors, to eventually be carried out by Dr. Burridge as an independent investigator.